Stencil



May 5, 1942. Q, NQERlS ZSZZSZS STENCIL Filed Jan. 3l, 1941 3Sheets-Sheet 2 XNVENTOR 1 50W/150 0 /Vome/s f "S P l ATTORNEY May 5,1942. O, NORM 2,282,203

STENCIL Filed Jan. 3l, 1941 3 Sheets--Sheel 3 Patented May 5, 11942UNITED STATES PATENT OFFICE (Cl. 10i-127) 5 Claims.

defined and unbroken, and the edges of larger areas are clearly demarkedand free from the ragged or ,saw-toothed appearance which oftencharacterizes work done with the ordinary screen stencil.

The objects Will be presently more clearly brought out a's the stencilitself and the mode of constructing it are explained in connection withthe drawings.

Referring to the drawings,

Fig. 1 is an isometric view showing a portion of stencil base whichconsists preferably of electroformed foraminous sheet. On the sheet isindicated an area in the form of an annulus which may be taken forpurposes of illustration as the design that is to be printed orimpressed;

Fig, 2 is an isometric view of a portion of the screen of Fig. 1 showingthe screen of Fig. 1 covered with three layers of materials partlybroken away;

Figs. 3, 4, and 5 show successive steps in the production of the nalstencil;

Fig. 6 illustrates a further step whereby the design is opened upthrough the stencil to permit free passage of the printing agent;

Fig. 7 shows the completed stencil;

Figs. 8, 9, 10, and 11 show a modied process of producing the stencil ofFig. 7.

Figs. 12, 13, 14, and 15 illustrate successive steps in a third methodcf effecting the objects of the invention.

It is to be realized that the drawings are on a vastly' larger scalethan would be employed in practice. Usually the base screen would havein the order of from 25 to 100 meshes to the linear inch, and as much aspossible of the area would be open, the limit of open area obviouslybeing fixed by the strength of the material, the nature of the use to.which the stencil is to be put, etc. In most cases the design would beof a more elaborate nature than what I show in the drawings. However,the principle involved in my invention is the same regardless of theelaborateness of the design, and so I have selected a very simple one bywhich to explain the process and the iinal product.

' the usual.

Referring specically to the drawings,

Fig. l shows a portion of an electroformed screen consisting of thewires l0 intersected normally by the wires II. Preferably, as statedabove, the open areas l2 are as large as possible consistent withsuitable structural strength. Such a screen and a method of producing itare illustrated and described in my United States Patent No. 2,166,366,issued July 18, 1939, and therefore it is not necessary to go intodetails as to how the screen itself is produced.

In using the term wires to describe the component parts of the screenstructure, I am aware that the word is used in a sense somewhat beyondHowever, it is a fact that a true wire structure, such as woven wirescreen, would serve my purposes, although, as I have found, notassatsfactorily as does the electroformed screen.

In screen of the electroformed type, what I have termed wiresarefrequently known as lands In general, such screen structures may betermed mesh fabric, which includes, in the ordinary accepted meaning ofthe term, not only woven fabric but also that which is punched, etchedor electroformed as well.

To make the process clear, I have shown on Fig. 1 in dotted lines anannular area which will correspond with the open area of the completedstencil, the remaining areas of the stencil of course being blocked out.as will. be presently described, by imperforate sheet superimposedthereon.

In order to carry through the description it should be explained that itinvolves selective etching-i. e., the employment of etching agents thatcorrosively react on one material to the eX- clusion of another, and toavoid complicated language it will be assumed that the material of thebase screen is of nickel. On the nickel screen which will eventuallyserve as a backing for the layers of imperforate material to be laidthereon, is deposited a layer I3 of copper, the copper completelycovering the `,base screen `itself to a substantial thicknesswhich..however, is not critical. This copper is applied preferably byelectroforming, the bottom (with referencevto the orientation vof thescreen as shown in the drawings) being suitably masked according tomethods wellknown in the electroplating and electroforming arts. Anincident to the electroforming step (unless the holes are rst filledwith electrically non-conductive material). the copper not only overliesthe base screen but it also extends into the holes. As will be vapparenthowever, as the description goes on, it is merely necessary that ing I5of glue or shellac rendered light-sensitive by the presence of ammoniumbichromate.. The well-known coatings known as Coldtop and Gluetop servethe purpose very well. The particular type of coating is not howeverimportant as long as it is resistant tothe etching agent f The result isthat in printing, the' design ao-v which is employed to etch the nickel,as will be v explained.

The next step (see Fig. 3) is to photoprint the design on the coating ofemulsion, whichis done `by the plate I B exhibiting a positive of thedesign indicated by shading in Fig. 3. In other words, the shadedportion is opaque to light and the remaining portion is transparent. Theprinting' being completed, the result is that the area of theAlight-sensitive coat `protected by the shaded area of the plate I6 fromthe light source is unaffected, while the remaining area is hardened andinsoluble to water. The light-sensitive coat is then developed bywashing in water if the glue top be used, consequently exposing .thenickel I4, as indicated at I1 (see Fig. 4),

Where previously covered by the design area. 1f shellac be used, itwould be washed out with an alcoholic preparation sold under the tradename of` Chemco Glascote Developer. The steps of producing the design onthe sensitized coat and the steps of developing and exposing the nickelto correspond with it are well-known and need no detailed or furtherdescription,

does not affect the developed-coating I5, and

therefore the area of its corrosive action is accurately delimited -bythe edges of the latter. The nickel'layer is preferably very thin-say,in the order of .003" and, since the etching process is arrested whenthe nickel has been completely etched through to the copper layer I3,orperhaps when it has progressed very slightly into the copper, andsince there is no opportunity for any perceptible undercutting of thenickel during the brief period of action, the edges of the nickel thatdelimit the design are smooth and well defined. 4 The result of theforegoing etching step is shown in Fig. 5, where the nickel has beenetched completely through andthe area IBfof the copper surface below itis exposed.

The next step is toycontinue the etching with an agent that will actcorrosively on the copper of the layer I3 but will not affect thematerial of the layer` I4 or the material of the base screen. Asuitableetching agent for this purpose is chromic acid which activelyetches copper but which, since it has no eiect or appreciable effect onnickel, will not attack either the layer I4 or the base screen itself.'I'his etching step is carf previously described.

ried to the point where the copper of the layer I3 is etched until it isfree and clear of the lands of the base screen; so that ink or othersubstance to be forced through the stencil to print the desired designwill freely travel through the conducting passages between the screenand the copper and emerge in uniform volume and in e solid continuousmass on to the surface being pri-nted. 'I'he general conformation of theink passage is shown in Fig. 6, the spacing between the copper and thescreen lands being indicated by the numeral I9.

pears in a complete unbroken line, the ink or other substance passingthrough the stencil unobstructed by the lands of the screen. Prior toactually employing the stencil for printing purposes, the developedcoating I5 is removed. by the application of a suitable agent such, forexample, as caustic potash. The completed stencil is shown in Fig. 7,its printing face-i. e., the

face that contacts with the work being upperv most as shown in thedrawings.

The advantages of the stencil can now be brought out more clearly thanbefore. By referring back to Fig.. l, it will vbe seen that, when the/ldesignv includes fine lines such as the annular figure which I am usingas anr illustration, the ordinary process of simply blocking out thestencil to form the'design leaves these fine lines in many casesoverlying and blocked by portions of the lands.` This is brought out inFig. l, where, vfor example, a portion of the annulardesign traversesfor a short distance the land |08 as indicated. It also crosses variousother lands and is blocked'out by the land IIa. Consequently, when astencil of this simple form is used for printing neline figures,especially where the lines are about the width of the screen land orless, the lines, when printed, appear broken for the reason that the inkis not delivered at those portions where the design is blocked out bythe screen lands. My stencil, however, is distinguished from thestandard construction which I have described in that in the former thene line discharge orifice for the ink is open at all points to thesourcev of supply on the opposite or rear side of the stencil, and thusthe ink or the like .comes through freely, passing around the lands ofthe screen and thence through the discharge orifice in uniform volumevand in an unbroken mass. As an extension of the foregoing, the stencilalso has denite advantages even where Aan area covering many meshes ofscreen is open,

in that the edges of the printed design do not present a ragged orsaw-tooth lappearance as they would and do where they are partially cutintoby the screen lands. v

Figs. 8-11, both inclusive, show of the process. In this case, asv inthe previous case, the base screen may be assumed to be of nickel withthe copper deposit I3 completely lilling the holesand covering thescreen itself. From then on the process varies from the process vInstead of applyingV to the copper a 'coat of nickel, then a sensitizedcoat, and printing with apositive of the design, the light-sensitizedlayer 20 is laid directly on the copper I3. Printing is then'done by aplate 2I which is a negative of the design, the shaded areas 22 beingopaque and the unshaded area 23 in the form of the desired design beingtransparent." The result after printing and developing is shown in Fig.y9 in which the copper surface of the layer I3 is exposed and there issua modification Y in the nickcl plate 25.

perimposed thereon in theform of a hardened sensitized coat the area 24,24. The structure of Fig. 9 is then subjected to an electro-formingoperation, whereby the layer 25 of nickel is adherently laid on thecopper. The hardened coat 24 is then removed by the application of a.suitable agent such as caustic potash, leaving the area 26 of the coppersurface exposed in the form of the design. The structure of Fig. is thensubjected to an etching process, the etching agent being of a characterthat does not aiiect the nickel of the layer 25 or the material of thescreen itself. As in the process of Figs. 1 7, this agent may be Chromicacid and the etching is carried through to the bottom of the plate,creating a lrce passage for ink or the like from the rear face to andout ol the annular orifices In other words, the ultimate result is thestencil of Fig. 11 in all essential respects similar in construction andmode of operation to the stencil of Fig. 7.

In explaining the invention I have up to this point preferred, for thesake of clarity, to name a combination of specific materials indescribing a way in which it may be carried out. However, it will beseen that the underlying principles do not necessarily involve the useof thev specific materials that I have named. For example, if the basescreen were of copper instead of nickel, the layer I3 could be of Zincinstead of copper and the layer I4 of copper in place of nickel. In suchcase, however, the selection of etching agents would need to be adaptedto bring about the selective actions that arenecessary. In the case justsupposed, for example. the photographic printing might be through apositive transparency of the design as shown in Fig. 3. The firstetching agent could be ferric chloride as before, for the reason that,while it attacks the copper, it does not affect the developed coatingI5. This first etching would remove or dissolve the copper and perhaps,to a very slight depth, the zinc. The next etching must, however, be ofsuch a nature as to etch the zinc but not affect the copper, for thereason that the base screen, which is of copper, must be preserved andalso the edges of the copper layer must remain intact. A suitableetching agent for this purpose is sulphuric acid diluted with water,which actively attacks zinc but does not affect copper.

If other combinations of metals than nickel or zinc and copper or othertypes of sensitized coating are used, it is necessary to select etchingagents that will act selectively in accordance with the foregoingprinciples. As to the combination of nickel and copper, I have selectedthem as preferable because they are adaptable for stencil purposes, arereadily etched selectively, are comparatively inexpensive, and lendthemselves readily to electroforming process. A further example might begiven, such as the combination of a nickel base screen, a layer ofcopper superimposed thereon, and a second layer or facing of chrome. Inthis case the chrome would be etched or could be etched down to thecopper by hydrochloric acid. The second etching step through the copperto expose the base screen can then be accomplished by means of a secondagent consisting of a mixture of sulphuric and chromic acids and watere.g.,

Sulphuric acid lbs 2 Chromic acid lb-- 1 Water -gals-- 10 This mixturewill not attack nickel except possibly very slowly, and the etching ofthe copper by it would, in practice, be arrested by the operator beforethe nickel of the base screen became appreciably affected.

A third method of accomplishing the 'objects of the invention isillustrated by Figs. l2-15. This method may be best understood byreference to Fig. 9. Up to Fig. 9 it is similar to the second methodillustrated in Figs. 8-11. Starting therefore with Fig.9, a very thinlayer 3 0 of nickel is electrolytically deposited on the rear face ofthe structure, the purpose of which will presently appear. Followingthis step the copper I3 is etched away by, for example, chromic acid,but, inasmuch as it is partially protected by the band of solidiiiedglue 24, the portions of the copper beneath the band are left as shownin Fig. 13,. the etching step of course being arrested before thoseportions are entirely removed. By this step the wires of the basescreenA and also the thin layer 30 of nickel are exposed and are capableof receiving a heavy adherent deposit 3I of nickel, as shown in Fig. 14.After the heavy deposit of nickel has been applied, theband 24 ofdeveloped glue is removed by the application, for example, of causticpotash, andA then the exposed copper is etched out by chromic acid whichdoes not affect the nickel deposit 3l. After removing the thin nickellayer 30 to open the ink passages, which may be done by brushing4 (sinceits thickness is only in the order of say .000O5), ,thev result is shownin Fig. 15, where the fine line of the design is not blocked against thepassage of ink by any of the wires of the screen. The sameprinciples ofselectivity should be followed in choosingmetals, etching agents, andother materials in carrying out the third method which I describe asinthe case of the first and second methods.

In applying the successive layers of metal in my several methods,electroforming acts most satisfactorily. Where etching is referredl to,electrolytic depleting is included wherever the process is applicable.

I have described above certain embodiments of my invention, but I wishit to be understood that these are illustrative and vnot limitative andthat I reserve the right to make various changes in form, construction,and arrangement of partsthatstill fall within the spirit and scope of myinvention as set forth in the claims.

I claim:

1. A screen stencil comprising metal mesh fabric having an area of openmesh forming a design, said area being delimited by areas of solid sheetmetal covering the fabric and lling the meshes where covered, saiddesign comprising a band atleast as narrow as the wires of the fabric,vand passages leading from the bands around the wires and opening at theopposite face of the stencil. Y

2. A screen stencil comprising metal mesh fabric provided with areas ofimperforate sheet metal superimposed thereon, said areas being separatedby open mesh areas conforming to the design to be printed, said openmesh areas comprising bands narrower than the wires of the fabric, thesaid narrow areas communicating with the rear face of the fabric bymeans of passages leading to and opening at said rear face and aroundsaid portions of the wires as are directly beneath [the said narrowareas'.v

3. A screen stencil, comprising a metallic base screen with areasblocked out on one face by a layer of imperforate metal superimposedthereon, leaving exposed areas of the base screen denning the design tobe printed, some of the ex'posed areas being of a width notsubstantially exceeding that of the base screen wires underlying them,liquid communication through the stenci1.frorn last-mentioned areasAbeing established by passages leading from them through meshes ofthe'base screen adjacent said underlying Wires. 1 4. A screen stencil,comprising metal meshlO fabric and having a printing face of open mesh`areas conforming to the design to be printed and delimited by closedmesh areas of imperforate metal, some of the design areas being of awidth not substantially exceeding that of the wires of the fabricunderlying them, the stencil being provided with liquid feeding passages'areas of the -fabric conforming to the design to be printed, some ofthe design areas being of a width not substantiailyrexceeding the widthof the'wires of the fabric, the stencil being provided with liquidfeeding passages leading from the last-mentioned design areas, thencearound the wires underlying said areas and emerging at the opposite faceof the stencil through the meshes f yadjacent said underlying wires.

EDWARD o. NoRRIs. l

